1. Field of the Invention
This invention relates to the synthesis of ammonia.
2. Prior Art
A book entitled "Ammonia Part III", edited by A. V. Slack and G. Russell James, published by Marcel Decker, Inc., 1977, describes the commercial ammonia processes of fourteen (14) companies in Chapter 9, pages 291 to 369 inclusive. Most of the commercial processes use a quench type ammonia converter. In a quench type converter, the synthesis gas is passed through a plurality of catalyst beds with a part of the synthesis gas being directed and admixed with the effluent from the catalyst beds to cool the effluent before passing to the next catalyst bed. The disadvantage of this type of ammonia converter is that all of the synthesis gas does not pass through all of the catalyst beds. Quench type converters are also disclosed in U.S. Pat. Nos. 3,784,361; 3,372,988; 3,567,404; 3,694,169; 3,475,136; publications "Radial Converter Shows Big Benefits for Ammonia", Petroleum International, Nov. 1974, Vol. 14, No. 11, pp. 72-76; and Nitrogen, May/June 1976, Vol. No. 101, pp. 42-43. Radial type ammonia converters of Topsoe are also disclosed as having one or two catalyst beds (FIG. 26, Topsoe singular bed radial converter and FIG. 27, Topsoe two bed radial converter) on pages 346 and 347 of the book "Ammonia Part III" referred to hereinabove. All of these Topsoe converters appear to utilize quench gas, at least in part, to control the temperature of catalyst bed effluent. The use of secondary feed and recycled effluent mixing is disclosed in U.S. Pat. Nos. 3,918,918; 3,998,932; and, 3,941,869.
The book "Ammonia Part III" also discloses ammonia converters having indirect heat exchange between catalyst beds, however, in each of these designs, the synthesis gas is passed downwardly or axially through the beds (FIG. 12, OSW Ammonia Converter, Page 315) which causes large pressure drops. Synthesis gas flow is also axial in the Braun process as discussed on pp. 364-365, FIG. 39, of the book. See also, Nitrogen, No. 100, March/April, 1976.
The ammonia synthesis pressure of all of the ammonia commercial processes disclosed in the "Ammonia Part III" book are in excess of 150 atmospheres and in most cases exceed 200 atmospheres. On page 354, it is stated that "[T] the present trend of design of ammonia plants is to higher loop pressure in order to get higher ammonia conversion per pass in the converter." The only disclosure of 100 atmospheres for ammonia synthesis is in regard to certain developmental work of the mid 1920's, although it is stated that the plants using this work were all built with 150 atmospheres as the ammonia synthesis pressure. Synthesis pressures of 1 to 68 atmospheres are incidentally disclosed in U.S. Pat. No. 2,550,389, and pressures of 20 to 400 atmospheres are disclosed in U.S. Pat. No. 3,957,449, although no commercial plant is known which operates at low pressures, i.e. less than 100 atms. Patents of general interest include U.S. Pat. Nos. 3,279,153; 3,031,274; 3,754,078; and, Great Britain Pat. No. 1,115,952.